Long Term Evolution (LTE) is a mobile network technology standard based on a 3GPP standard. It is a set of enhancements to the Universal Mobile Telecommunications Systems (UMTS) and is designed to increase data rates for mobile wireless users, improve user throughput and make more efficient use of the radio frequency spectrum. LTE-Advanced is currently being standardized by the 3GPP as an enhancement of LTE.
FIG. 1 shows the configuration of a heterogeneous LTE-Advanced or LTE Rel-10 mobile communication network 10. In the system 10, base stations 12, 14, also known as evolved Node Bs (eNode B), support communication for multiple User Equipments (UEs) 16, 18, for example mobile phones, laptops, personal digital assistants. The base stations 12, 14 are fixed and each provide communication coverage for a particular geographical area. Base station 12 is a femto cell, which connects to the service provider's network via broadband, and provides coverage over component carriers CC #0 and CC #1. Base station 14 is a macro cell which provides radio coverage over component carriers CC #0 and CC #1 over different distances for each component carrier.
In the downlink channel, from the base stations 12, 14 to the UEs 16, 18, the LTE standard uses Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a digital multi-carrier modulation method that uses a large number of closely spaced orthogonal sub-carriers to carry data. Orthogonal Frequency Division Multiple Access (OFDMA) is employed as a multiplexing scheme in the LTE downlink. In OFDMA, individual UEs are allocated sub-carriers for a predetermined amount of time. This allows simultaneous data transmission from several users.
The downlink channel supports physical channels, which convey information from higher layers in the LTE stack. Two physical downlink channels are the Physical Downlink Shared Channel (PDSCH), which is used for data transmission and the Physical Downlink Control Channel (PDCCH), which is used for transmitting control information. Scheduling of downlink data reception (in PDSCH) or uplink data transmission in the Physical Uplink Shared Channel (PUSCH) to the UE is typically performed through downlink control signaling using the PDCCH.